1. FIELD OF THE INVENTION
The present invention relates to a method of bonding alumina to a metal and, more particularly, to a method of bonding alumina to a metal which method is suitable for use in producing, for example, a mechanical structural element or an electronic element in which alumina and a metal must be bonded together at a temperature as low as possible.
2. DESCRIPTION OF THE PRIOR ART
A method of the prior art for bonding alumina and a metal is described in the specification of British Pat. No. 761,045. The method comprises the steps of: applying or forming on at least one of the surfaces of the material to be bonded a film or skin of cuprous oxide (Cu.sub.2 O); positioning the material to be bonded so that the surfaces thereof to be bonded are in contacting relation; and heating the assembly to a temperature between the melting point of copper (1083.degree. C.) and the melting point of cuprous oxide (1235.degree. C.) so as to achieve the bonding thereof through the reaction between the cuprous oxide, molten copper and substrate.
According to the above-described method, however, it is necessary to effect heating at a high temperature, lower than 1,230.degree. C., which heating causes a thermal stress due to the difference in thermal expansion between alumina and a metal when they are cooling down after being bonded together. Therefore, the alumina is easily cracked, resulting disadvantageously in a lowering of reliability in strength. Further, the metal may be thermally deformed on heating, causing the dimensional accuracy of a product to be deteriorated.